Metal gasket

1. A metal gasket assembly comprising:

an annular metal gasket; and

a pair of housings, wherein

when the annular metal gasket is sandwiched between the pair of housings, the annular metal gasket seals an internal space of the housings and prevents entrance of external foreign matter into a crevice between one of the housings and the annular metal gasket,

the annular metal gasket includes:

an annular straight portion in which an entire surface from an inner peripheral edge portion to an outer peripheral edge portion is formed into a planar shape;

a plurality of flange portions integrally provided as a part of the annular straight portion on a same plane, and the plurality of flange portions protrudes parts of the outer peripheral edge portion;

a bolt hole provided in each of the plurality of flange portions; and

a bent bead portion provided so as to be directed obliquely outward and contacting the one of the housings, and the bent bead portion is integrally provided in the outer peripheral edge portion of the annular straight portion including the plurality of flange portions,

the bent bead portion is provided throughout an entire outer peripheral edge of the annular straight portion including the plurality of flange portions,

the bent bead portion functions as both an inward seal sealing the internal space of the housings and an outward seal preventing the entrance of the external foreign matter into the crevice between the one of the housings and the annular metal gasket,

an outer end of the bent bead portion of the annular metal gasket is exposed to an outside of the pair of housings where the external foreign matter that includes salt water exists,

the bent bead portion is an only bead in the annular metal gasket and a bending point of the annular straight portion and the bent bead portion is an only bending point in the annular metal gasket, and

in the bent bead portion, a bead width from the outer peripheral edge portion to an outermost peripheral edge of the annular metal gasket is set within a range of 0.5 to 1.3 mm and a rise height is set within a range of 0.25 to 0.7 mm.

2. The metal gasket assembly according to claim 1 , wherein

the annular metal gasket is an annular metal gasket that is laminated, in which rubber layers are deposited to surfaces of a metal plate.

3. The metal gasket assembly according to claim 2 , wherein

the metal plate of the annular metal gasket is made of steel.

4. The metal gasket assembly according to claim 1 , wherein

the bead width is less than a width of the annular straight portion.

5. The metal gasket assembly according to claim 1 , wherein

a bent angle between the bent bead portion and the annular straight portion is defined by a trigonometric formula:

θ=180°−tan −1 ( h/w ),

where

θ is the bent angle,

h is the rise height, and

w is the bead width.

6. The metal gasket assembly according to claim 5 , wherein

when the bead width is within the range of 0.5 to 1.3 mm and the rise height is within the range of 0.25 to 0.7 mm, a range of the bent angle calculated according to the trigonometric formula is within 125.5° to 169.1°.

7. The metal gasket assembly according to claim 1 , wherein

the plurality of flange portions is disposed at equal intervals around a circumference of the annular metal gasket.

8. The metal gasket assembly according to claim 7 , wherein

the plurality of flange portions includes four flange portions.

9. The metal gasket assembly according to claim 1 , wherein

the bent bead portion extends obliquely downward in a linear direction from the outer peripheral edge portion of the annular straight portion.

10. The metal gasket assembly according to claim 1 , wherein

the inner peripheral edge portion of the annular straight portion forms an outer periphery of a circular opening of the annular metal gasket.

11. The metal gasket assembly according to claim 1 , wherein

in a cross section of the annular metal gasket, an entirety of the bent bead portion extends in a single direction so that a single bent angle is formed between the bent bead portion and the annular straight portion, and the bead width is only measured in the bent bead portion.

12. The metal gasket assembly according to claim 1 , wherein

the bead width is measured from an outermost peripheral edge on a top surface of the annular metal gasket to an edge between the bent bead portion and the annular straight portion that is on the top surface of the annular metal gasket, and the bead width is measured in a direction in which the annular straight portion extends.

13. The metal gasket assembly according to claim 1 , wherein

the rise height is measured from an outermost peripheral edge on a top surface of the annular metal gasket to an edge between the bent bead portion and the annular straight portion that is on the top surface of the annular metal gasket, and the rise height is measured in a direction perpendicular to a direction in which the annular straight portion extends.

14. The metal gasket assembly according to claim 1 , wherein

the pair of housings include an aluminum material, and

the bent bead portion prevents entrance of the salt water into the crevice between the one of the housings and the annular metal gasket, to prevent corrosion in the crevice due to ionization of the aluminum material by the salt water.

15. An annular metal gasket which is sandwiched between a pair of housings and seals an internal space of the housings and prevents entrance of external foreign matter into a crevice between one of the housings and the annular metal gasket, the annular metal gasket comprising:

an annular straight portion in which an entire surface from an inner peripheral edge portion to an outer peripheral edge portion is formed into a planar shape;

a plurality of flange portions integrally provided as a part of the annular straight portion on a same plane, and the plurality of flange portions protrudes parts of the outer peripheral edge portion;

a bolt hole provided in each of the plurality of flange portions; and

a bent bead portion provided so as to be directed obliquely outward and contacting the one of the housings, and the bent bead portion is integrally provided in the outer peripheral edge portion of the annular straight portion including the plurality of flange portions,

the bent bead portion is provided throughout an entire outer peripheral edge of the annular straight portion including the plurality of flange portions,

the bent bead portion functions as both an inward seal sealing the internal space of the housings and an outward seal preventing the entrance of the external foreign matter into the crevice between the one of the housings and the annular metal gasket,

the bent bead portion is an only bead in the annular metal gasket and a bending point of the annular straight portion and the bent bead portion is an only bending point in the annular metal gasket,

an outermost peripheral end surface of the bent bead portion is an exposed surface that is exposed to an outside of the pair of housings where the external foreign matter that includes salt water exists, and

in the bent bead portion, a bead width from the outer peripheral edge portion to an outermost peripheral edge of the annular metal gasket is set within a range of 0.5 to 1.3 mm and a rise height is set within a range of 0.25 to 0.7 mm.

16. The annular metal gasket according to claim 15 , wherein

the pair of housings include an aluminum material, and

the bent bead portion prevents entrance of the salt water into the crevice between the one of the housings and the annular metal gasket, to prevent corrosion in the crevice due to ionization of the aluminum material by the salt water.